Several studies have suggested that Secreted Frizzled-related protein 2 (Sfrp2), a Wnt pathway inhibitor, is a key mediator of myocardial wound repair and has been shown to inhibit myocyte apoptosis, induce angiogenesis and inhibit fibrosis. In several model systems, Sfrp2 is a regulator of differentiation yet no studies have been performed that directly address the significance of Sfpr2 in cardiomyocyte renewal and the role of Sfpr2 in cardiac progenitor cell (CPC) activation, proliferation and differentiation remains to be elucidated. The regulation of CPC expansion and differentiation is a fundamental but yet unclear aspect of cardiovascular biology and regenerative medicine. Our preliminary studies, both in vitro and in vivo, suggest CPCs are responsive to Wnt/Sfrp2 signaling. Our data suggest that Sfrp2 inhibits canonical Wnt3a signaling and enhances differentiation in adult c-Kit+/Sca1+ CPCs. Thus, the role of the Sfrp2 in modulation of adult cardiomyocyte renewal by a potential Sfpr2/Wnt interaction poses an intriguing question. To address this, we hypothesize that Sfrp2, by modulating Wnt canonical pathway, is a key regulator of cardiac progenitor proliferation and lineage specification. To test this hypothesis, using cultured CPCs, we will investigate in vitro the importance of Sfpr2 and Wnt3a on CPC proliferation and differentiation, and elucidate the role of the Wnt/b-catenin canonical signaling pathway. In vivo, we will extend these studies by evaluating the role of Sfrp2 on cardiomyocyte renewal by examining its effects on endogenous CPC fate. We will use a genetic fate-mapping study and lineage tracing protocols to examine the proliferation and activation of endogenous cardiac stem cells, the differentiation of these cells to cardiac mocytes and determine the role of Sfrp2 on these processes and we will enquire about the importance of the Wnt/b-catenin canonical signaling pathway in mediating the Sfrp2 effects on CPCs in vivo. At the conclusion of this research proposal we will have characterized the role of Sfrp2 signaling in adult cardiac stem cells providing novel insights about the pathways that regulate these cells and opening new opportunities about their modulation ex vivo or in vivo for therapeutic purposes. PUBLIC HEALTH RELEVANCE: Heart failure is a leading cause of mortality worldwide. Patients receive symptomatic treatment, and future biologically targeted therapy will depend on the discovery of new pathways that initiate, promote or potentially reverse the onset of heart muscle failure. In this grant application we propose to characterize Sfrp2 an inhibitor of Wnt signaling which, as our preliminary results indicate, is involved in activation and differentiation of cardiac progenitor cells. These studies should open new avenues for the better understanding of the mechanisms of heart failure and may lead to the potential development of novel therapeutic drugs for myocardial injury, hypertrophy and heart failure.